This invention relates to a process for producing cold rolled metal strip without hot band annealing and/or pickling of a hot processed strip prior to cold reduction. The process includes the sequential steps of tension leveling to crack scale and to flatten the hot processed metal strip, particle blasting the strip to ablatively remove the scale, positioning at least two cleaning brushes adjacent each surface of the strip and rotating the brushes in opposite directions relative to each other to remove any residual scale and to provide a predetermined roughness, polishing the cleaned surfaces with a brush to further reduce the roughness and cold reducing the cleaned strip so that the surfaces have a lustrous finish.
It is known to flatten hot rolled strip prior to cold reduction using a leveler. U.S. Pat. No. 4,872,245 discloses a process line for producing cold rolled steel strip from hot rolled strip. This patent discloses a hot rolled strip being elongated not more than 7% using a tension leveler having bridle and bending rollers to flatten the strip and to transversely crack scale. The elongated strip then is descaled by being passed through a pair of brushes and a pickle tank prior to cold reduction on a tandem mill.
It is known to cold reduce a hot rolled metal strip without recrystallization annealing and/or pickling of the hot rolled strip prior to cold reduction. U.S. Pat. No. 5,197,179 discloses a continuous process line for producing cold rolled stainless steel from hot rolled strip. This patent discloses a hot rolled strip being passed through a cold reduction tandem or reversing mill prior to annealing and pickling. Shot blasting may be used to help remove the scale.
It also is known to descale hot rolled metal strip without recrystallization annealing and/or pickling of the hot rolled strip prior to cold reduction. These descaling processes include one or more of the steps of tension leveling to crack the scale and flatten the hot rolled metal strip, grit blasting of the strip to remove the scale and mechanical brushing of the hot rolled strip prior to cold reduction. U.S. Pat. No. 5,606,787 discloses a continuous process line for producing cold rolled stainless steel from hot rolled strip. This patent discloses a hot rolled strip being passed through a tandem cold mill, a continuous annealing furnace, an optional molten salt bath, a pickler and an optional temper mill. Shot blasting and annealing of the strip prior to cold reduction is not required to produce a surface roughness less than 80 .mu.-inch after a single cold rolling. U.S. Pat. 5,554,235 discloses a continuous process line for producing cold rolled stainless steel without annealing or acid pickling a hot rolled strip prior to cold rolling on a tandem mill. This patent discloses a hot rolled strip being descaled by optionally stretching in a leveler to flatten the strip and to crack the scale and then using a shot blaster or a brush polisher to remove the scale prior to cold reduction. After cold rolling, the strip optionally may be passed through a conventional annealing furnace, another shot blaster, a brush polisher, a pickier and stretch levelers. Japanese patent application 55-133802 discloses a process line for producing cold rolled steel from hot rolled strip without annealing or acid pickling the hot rolled steel prior to cold rolling. The hot rolled strip is descaled using a tension leveler to crack the scale, passed through high pressure water sprays and finally through brushing rolls prior to passing through a cold rolling tandem mill.
Nevertheless, cold reduced steel surface flatness and roughness requirements are becoming increasingly more stringent for applications such as stainless steel sheet and tubing for fabrication into sinks, appliances, automotive trim, and the like. These applications often require cold reduced strip having no more than 20 I-units of flatness across the strip width and a surface roughness less than 0.4 micron Ra. The prior art processes for producing a cold rolled strip without hot band annealing and/or pickling prior to cold reduction do not produce the necessary flatness and surface smoothness to meet these customer requirements after cold reduction. Accordingly, there remains a need for an improved process for producing cold rolled metal strip, especially stainless steel, having lustrous surfaces without hot band annealing and/or pickling of a hot processed strip prior to cold reduction. There also remains a need for a process for descaling hot processed ferrous metal strip prior to cold reduction that does not require hydrochloric or sulfuric acid pickling. There also remains a need for a process for descaling hot processed stainless steel strip that does not require nitric acid, hydrofluoric acid or a fluoride compound.